Method for producing a master mixture based on carbonaceous nanofillers and superplasticiser, and the use thereof in hardenable inorganic systems

ABSTRACT

Hardenable inorganic systems such as cements, plasters, ceramics or liquid silicates, usable for example in the building trade, construction industry or oil drilling industry. The insertion of carbonaceous nanofillers, such as carbon nanotubes, for reinforcing mechanical properties and improving such systems. A method for producing a master mixture including at least one superplasticiser and carbonaceous nanofillers at a mass ratio of between 0.1% and 25%, preferably between 0.2% and 20%, in relation to the total weight of the master mixture, and also to said master mixture thus obtained and to the use thereof in a hardenable inorganic system with a view to producing materials with improved properties. The disclosure applies to the construction industry, the building trade and the oil drilling industry.

TECHNICAL FIELD

The present invention relates to curable inorganic systems, such ascements, plasters, ceramics or liquid silicates, which can be used, forexample, in the fields of building, construction or the oil drillingindustry.

The invention relates more particularly to the use of carbon-basednanofillers, such as carbon nanotubes, for reinforcing the mechanicalproperties and improving such systems.

The invention relates to a process for the preparation of a master batchbased on carbon-based nanofillers and a super plasticizer, to saidmaster batch thus obtained and to its use in a curable inorganic systemfor the purpose of preparing materials having improved properties.

The invention applies to the fields of construction, building ordrilling for oil.

TECHNICAL BACKGROUND AND TECHNICAL PROBLEM

Cement-based concrete remains the most widely employed material inconstruction. Despite the existence of solutions such as incorporationof metal reinforcements, there always exists a need to improve theproperties of concretes, whether their mechanical strength, theirresistance to aging or the control of the process of hydration of thecement forming the basis of concretes.

It has been demonstrated in preceding studies that the incorporation ofcarbon nanotubes in cements exhibits numerous advantages. This isbecause carbon nanotubes (or CNTs) confer improved mechanical propertiesand electrical and/or thermal conduction properties on any compositematerial in which they are present; in particular, their good mechanicalproperties and in particular their good properties of resistance toelongation are related in part to their very high aspect(length/diameter) ratios.

By way of example, in the document US 2008/0134942, the addition ofcarbon nanotubes at a content of greater than 0.2%, combined with theaddition of small contents of a plasticizer, makes it possible toreinforce cements in terms of resistance to compression and todeformation.

The document WO 2009/099640 describes a method for the preparation ofmaterials based on reinforced cement which consists in dispersing carbonnanotubes in a surfactant solution, in a surfactant/CNTs ratio ofbetween 1.5 and 8, using ultrasound, and then mixing the dispersion witha cement, so as to obtain a material comprising 0.02% to 0.1% of carbonnanotubes with respect to the cement. The carbon nanotubes employedpreferably have a diameter ranging from 20 to 40 nm and a length rangingfrom 10 to 100 μm. The surfactants are preferably polycarboxylate-basedsuperplasticizers. The CNT dispersion comprises more than 98% of waterand a low content of superplasticizer, generally of less than 1%. Thisdispersion is generally used rapidly after its preparation and is notstored. According to this document, the quality of the dispersion of theCNTs within the material results from the quality of the dispersion ofthe CNTs in the surfactant solution obtained by ultrasound. The effectsobtained are the increase in the Young's modulus and in the bendingstrength and also a reduction in the phenomenon of endogenous shrinkage.

Similar results with regard to the effects of carbon nanotubes as cementreinforcer are described in the document Cements & Concretes Composites,32 (2010), 110-150.

According to the document Materials Science and Engineering A, 527,(2010) 1063-1067, the mechanical reinforcement resulting from thepresence of the carbon nanotubes is also accompanied by thedensification of the cement.

Pervushin et al. have presented, at the Nano-technology for green andsustainable construction international conference, 14-17 Mar. 2010, inCairo, Egypt, the results obtained on the reinforcing of cement byvirtue of the incorporation of carbon nanotubes at contents as low as0.006% with respect to the cement, in the form of an aqueous dispersionobtained by hydrodynamic cavitation starting from powdered CNTs and asuperplasticizer. However, this study shows that these CNT dispersionsare not stable over time and thus have to be used rapidly for the cementreinforcing application; in addition, as the CNTs are generally providedin the form of agglomerated powder grains, the mean dimensions of whichare of the order of a few hundred microns, the handling thereof maypresent safety problems due to their pulverulent nature and theirability to generate fines in the plants where they are used.

In patent application WO 2012/085445, provision has been made tointroduce, into the curable inorganic system, carbon nanotubes not inthe powder form but in the form of a master batch of carbon nanotubescomprising a polymer binder. The process consists in preparing adispersion in water of carbon-based nanofillers starting from a masterbatch of carbon-based nanofillers and of a polymer binder, in thepresence of at least one superplasticizer, and in subjecting thisdispersion to a treatment by high-speed mixing, for example bysonication, by cavitation of the fluids or using a Silverson high shearmixer or a bead mill. The dispersion is introduced, as is or rediluted,into a curable inorganic system, such as a cement, to ensure a finalcontent of carbon-based nanofillers ranging from 0.001% to 0.02% byweight, preferably from 0.005% to 0.01%, with respect to the curableinorganic system. According to this process, the procedure for thedispersion still remains lengthy and difficult to carry out on a greaterscale, and the composite material obtained, such as a concrete,comprises a low content of a polymer binder, which may possibly affectthe properties thereof.

Consequently, the introduction of carbon nanotubes into cement-basedmaterials or any other curable inorganic system still raises a fewnegative points which have to be improved.

It is therefore desirable to have available a means which makes itpossible to simply and homogeneously distribute carbon nanotubes withina cement-based material or any other curable inorganic system for thepurpose of preparing composite materials of high mechanical strength andpreventing the cracks resulting from the aging of these materials.

Furthermore, due to their pulverulent nature and their ability togenerate fines in manufacturing plants, it is preferable to be able towork with CNTs in agglomerated solid form of macroscopic size.

The applicant company has discovered that these requirements could bemet by introducing carbon nanotubes into cement-based materials or anyother curable inorganic system via a master batch based on carbonnanotubes and on a superplasticizer. This is because the use of asuperplasticizer is always recommended in order to increase thecompactness and the mechanical strength of concretes and mortars and toimprove their fluidity and their handling.

The present invention thus consists in replacing the superplasticizerwith a superplasticizer doped with carbon nanotubes in the existingmanufacturing processes and devices of the building and constructionindustry and also in the oil field.

The process of the introduction of the carbon nanotubes according to thepresent invention is simple, fast and easy to carry out from anindustrial viewpoint while observing the constraints of health andsafety. It does not require modifying the conventional processes for themanufacture of composite materials based on curable inorganic systemswhich already use a superplasticizer as high water-reducing dispersingadditive, while resulting in materials which are denser and mechanicallyreinforced.

Furthermore, it is apparent to the applicant company that this inventioncan also be applied to other carbon-based nanofillers than carbonnanotubes and in particular to carbon nanofibers and to graphenes.

SUMMARY OF THE INVENTION

A subject matter of the present invention is thus a process for thepreparation of a master batch comprising at least one superplasticizerand from 0.1% to 25% of carbon-based nanofillers, expressed with respectto the total weight of the master batch, comprising:

(i) the introduction into a kneader and then the kneading ofcarbon-based nanofillers and of at least one superplasticizer,optionally in the presence of a water-soluble dispersing agent, in orderto form a homogeneous mixture in the solid form or in the pastycomposition form;

(ii) the extrusion of said mixture in the solid form in order to obtaina master batch in the solid form;

(iii) optionally the dispersion of said master batch in the solid formin a superplasticizer identical to or different from that of stage (i),or in a water-soluble dispersant, in order to obtain a master batch inthe form of a pasty composition;

(iv) optionally the introduction of the master batch in the form of apasty composition obtained in stage (i) or in stage (iii), into asuperplasticizer which is identical to or different from that of stage(i) or that of stage (iii), in order to obtain a master batch having alow content of carbon-based nanofillers.

According to one embodiment of the process according to the invention,stage (i) results directly in the preparation of a master batch in theform of a pasty composition, it being possible for said process toadditionally directly comprise stage (iv), in order to obtain a masterbatch having a low content of carbon-based nanofillers.

The invention also relates to a master batch comprising at least onesuperplasticizer and carbon-based nanofillers at a content by weight ofbetween 0.1% and 25%, preferably between 0.2% and 20%, with respect tothe total weight of the master batch, capable of being obtainedaccording to said process.

Another subject matter of the invention is a process for theintroduction of carbon-based nanofillers into a curable inorganicsystem, comprising at least the stage of introduction of water and of amaster batch as described above, separately or as a mixture, into akneading appliance comprising at least one curable inorganic system, inorder to ensure a content of carbon-based nanofillers ranging from0.0001% to 0.02% by weight, preferably from 0.0005% to 0.01% by weight,with respect to the curable inorganic system, and a water/curableinorganic system ratio by weight ranging from 0.2 to 1.5 and preferablyfrom 0.2 to 0.7.

The invention also relates to the composite materials based on curableinorganic systems capable of being obtained according to this processand to their uses in the field of construction and building, forpreparing mortars for bricklaying or interior and exterior coatings orfor manufacturing structural construction products, and in the field ofthe oil industry, for drilling applications.

Another subject matter of the invention is the use of a master batchbased on at least one superplasticizer and on 0.1% to 25% by weight ofcarbon-based nanofillers, with respect to the total weight of the masterbatch, for improving the resistance to freezing and to the diffusion ofliquid of a curable inorganic system, such as a cement, or for improvingthe adhesion between a curable inorganic system and metal or nonmetalreinforcements or reinforcers in the form of mineral fibers orreinforcers based on polymers, in structural construction products, orfor reducing the phenomena of microcracking due to the various stressesin structural construction products.

DETAILED DESCRIPTION

The invention relates to the field of curable inorganic systems, that isto say inorganic materials, such as cement bases, which, after mixingwith water, cure equally well in air as in water. The agglomerates ofthese materials which result therefrom, such as concretes, withstandwater and exhibit a compressive strength.

Any type of cement base as described in the standard EN-197-1-2000 isespecially concerned, in particular Portland-type cement, compositePortland cement, for example with limestone, with slag, with fly ash,with pozzolana, with calcined shale or with silica fume, blast furnacecement, pozzolanic cement, magnesia cement, or other anhydrite-basedcement, such as fluoroanhydrite cement, used alone or as a mixture,which constitute concretes, but also materials such as gypsum, whichforms the basis for plasters, or ordinary lime.

The invention can also be applied to inorganic materials, such as liquidsilicates and ceramics, which cure with heat at high temperature.

Preferably, the curable inorganic system is a cement base and, for thisreason, the detailed description will refer essentially to cement and toconcrete, for reasons of simplicity, it being understood that theinvention is not under any circumstances limited to this type of curableinorganic system.

The Carbon-Based Nanofillers

In the continuation of this description, the term “carbon-basednanofiller” denotes a filler comprising at least one component from thegroup formed of carbon nanotubes, carbon nanofibers and graphenes, or amixture of these in all proportions. According to the invention, it ispreferable to use carbon nanotubes as carbon-based nanofillers, alone oras a mixture with graphenes.

The carbon nanotubes participating in the composition of the masterbatch can be of the single-walled, double-walled or multi-walled type.The double-walled nanotubes can in particular be prepared as describedby Flahaut et al. in Chem. Com. (2003), 1442. For their part, themulti-walled nanotubes can be prepared as described in the document WO03/02456.

The carbon nanotubes employed according to the invention usually have amean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm,more preferably from 0.4 to 50 nm and better still from 1 to 30 nm,indeed even from 10 to 15 nm, and advantageously a length of more than0.1 μm and advantageously from 0.1 to 20 μm, preferably 0.1 to 10 μm,for example of approximately 6 μm. Their length/diameter ratio isadvantageously greater than 10 and generally greater than 100. Thesenanotubes thus comprise in particular “VGCF” (Vapor Grown Carbon Fibers)nanotubes. Their specific surface is, for example, between 100 and 300m²/g, advantageously between 200 and 300 m²/g, and their bulk densitycan in particular be between 0.01 and 0.5 g/cm³ and more preferablybetween 0.07 and 0.2 g/cm³. The multi-walled carbon nanotubes can, forexample, comprise from 5 to 15 sheets and more preferably from 7 to 10sheets.

These nanotubes may or may not be treated.

An example of crude carbon nanotubes is in particular the trade nameGraphistrength® C100 from Arkema.

These nanotubes can be purified and/or treated (for example oxidized)and/or ground and/or functionalized.

The grinding of the nanotubes can in particular be carried out undercold conditions or under hot conditions and can be carried out accordingto the known techniques employed in devices such as ball mills, hammermills, edge runner mills, knife mills, gas jet mills or any othergrinding system capable of reducing the size of the entangled network ofnanotubes. It is preferable for this grinding stage to be carried outaccording to a gas jet grinding technique and in particular in an airjet mill.

The crude or ground nanotubes can be purified by washing with a sulfuricacid solution so as to free them from possible residual inorganic andmetallic impurities, such as, for example, iron, originating from theirprocess of preparation. The ratio by weight of the nanotubes to thesulfuric acid can in particular be between 1:2 and 1:3. The purificationoperation can furthermore be carried out at a temperature ranging from90 to 120° C., for example for a period of time of 5 to 10 hours. Thisoperation can advantageously be followed by stages of rinsing with waterand of drying the purified nanotubes. In an alternative form, thenanotubes can be purified by heat treatment at a high temperature,typically of greater than 1000° C.

The nanotubes are advantageously oxidized by being brought into contactwith a sodium hypochlorite solution including from 0.5 to 15% by weightof NaOCl and preferably from 1 to 10% by weight of NaOCl, for example ina ratio by weight of the nanotubes to the sodium hypochlorite rangingfrom 1:0.1 to 1:1. Oxidation is advantageously carried out at atemperature of less than 60° C. and preferably at ambient temperature,for a period of time ranging from a few minutes to 24 hours. Thisoxidation operation can advantageously be followed by stages offiltering and/or centrifuging, washing and drying the oxidizednanotubes.

The nanotubes can be functionalized by grafting reactive units, such asvinyl monomers, to the surface of the nanotubes. The constituentmaterial of the nanotubes is used as radical polymerization initiatorafter having been subjected to a heat treatment at more than 900° C., inan anhydrous and oxygen-free environment, which is intended to removethe oxygen-comprising groups from its surface. It is thus possible topolymerize methyl methacrylate or hydroxyethyl methacrylate at thesurface of carbon nanotubes.

Use is preferably made, in the present invention, of crude carbonnanotubes which are optionally ground, that is to say nanotubes whichare neither oxidized nor purified nor functionalized and which have notbeen subjected to any other chemical and/or heat treatment.

The carbon nanofibers are, like the carbon nanotubes, nanofilamentsproduced by chemical vapor deposition (or CVD) from a carbon-basedsource which is decomposed on a catalyst comprising a transition metal(Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures from 500to 1200° C. However, these two carbon-based fillers differ in theirstructure (I. Martin-Gullon et al., Carbon, 44 (2006), 1572-1580). Thisis because carbon nanotubes consist of one or more graphene sheets woundconcentrically around the axis of the fiber to form a cylinder having adiameter of 10 to 100 nm. In contrast, carbon nanofibers are composed ofrelatively organized graphitic regions (or turbostratic stacks), theplanes of which are inclined at variable angles with respect to the axisof the fiber. These stacks can take the form of platelets, fishbones ordishes stacked in order to form structures having a diameter generallyranging from 100 nm to 500 nm, indeed even more.

Preference is furthermore given to the use of carbon nanofibers having adiameter from 100 to 200 nm, for example of approximately 150 nm (VGCF®from Showa Denko), and advantageously a length from 100 to 200 μm.

The term “graphene” denotes a flat, isolated and separate graphite sheetbut also, by extension, an assemblage comprising between 1 and a fewtens of sheets and exhibiting a flat or more or less undulatingstructure. This definition thus encompasses FLGs (Few Layer Graphene),NGPs (Nanosized Graphene Plates), CNSs (Carbon NanoSheets) and GNRs(Graphene NanoRibbons). On the other hand, it excludes carbon nanotubesand nanofibers, which are respectively composed of the coaxial windingof one or more graphene sheets and of the turbostratic stacking of thesesheets. Furthermore, it is preferable for the graphene used according tothe invention not to be subjected to an additional stage of chemicaloxidation or of functionalization.

The graphene used according to the invention is obtained by chemicalvapor deposition or CVD, preferably according to a process using apulverulent catalyst based on a mixed oxide. It is characteristicallyprovided in the form of particles with a thickness of less than 50 nm,preferably of less than 15 nm, more preferably of less than 5 nm, andwith lateral dimensions of less than a micron, preferably from 10 nm toless than 1000 nm, more preferably from 50 to 600 nm, indeed even from100 to 400 nm. Each of these particles generally contains from 1 to 50sheets, preferably from 1 to 20 sheets and more preferably from 1 to 10sheets, indeed even from 1 to 5 sheets, which are capable of beingseparated from one another in the form of independent sheets, forexample during a treatment by ultrasound.

The Superplasticizers

The use of high water-reducing superplasticizers makes it possible toreduce the water of the concrete at equal consistency, resulting in thesuppression of a large volume not mobilized by the water necessary forthe hydration of the cement. The addition of a superplasticizer at alevel of 1% to 2% of the weight of cement makes it possible tosignificantly reduce the volume of water necessary. The presence of asuperplasticizer thus makes it possible to increase the compactness andthe mechanical strength of concretes and mortars, while improving theirfluidity and their processing. Thus, the content of superplasticizerwill be adjusted as a function of the final use of the curable inorganicsystem; for example, in the case of fluid cement-based concrete intendedfor injections, the content of superplasticizer will be greater in orderto render the concrete pumpable.

Due to the properties introduced during the use of a superplasticizer,these products have now become essential in the fields of construction,building and oil drilling operations.

Mention may be made, as examples of superplasticizer which can be used,of:

-   -   sulfonated salts of polycondensates of naphthalene and        formaldehyde, commonly known as polynaphthalenesulfonates or        naphthalene-based superplasticizers;    -   sulfonated salts of polycondensates of melamine and        formaldehyde, commonly known as melamine-based        superplasticizers;    -   lignosulfonates having very low sugar contents;    -   polyacrylates;    -   products based on polycarboxylic acids, in particular polyether        polycarboxylate salts;    -   and their corresponding aqueous solutions.

Use is made in particular of naphthalene-based superplasticizers, suchas the condensation products of naphthalenesulfonic acid withformaldehyde, which comprise oligomers of naphthalene methyl sulfonateand sodium naphthalenesulfonate, or superplasticizers of the family ofmodified sodium lignosulfonates, or of the family of polycarboxylicacids, in particular polyether polycarboxylate salts, or also the familyof acrylic copolymers.

Use may be made, for example, of the commercial products Megalit C-3,Superplast C-3 or Polyplast SP-1, the products of the Ethacryl range orthe product XP 1824 from Coatex.

The superplasticizers are generally commercially available in the formof a more or less viscous aqueous solution having a more or less highviscosity.

The Master Batch

According to the present invention, the term “master batch” refers to amatrix of at least one superplasticizer in which carbon-basednanofillers are dispersed at contents ranging from 0.1% to 25%,preferably from 0.2% to 20%, with respect to the total weight of themaster batch, the physical appearance of the master batch varyingaccording to the content of carbon-based nanofillers.

A master batch comprising from 0.1% to 1% of carbon-based nanofillerscan be compared to a superplasticizer doped with carbon-basednanofillers.

Thus, a master batch in the solid form generally comprises from 10% to25% of carbon-based nanofillers; in this case, the solids content,except for the content of carbon-based nanofillers, is generally between30% and 40%.

A master batch in the pasty composition form generally comprises from 2%to 10% of carbon-based nanofillers. The master batches having a lowcontent of carbon-based nanofillers, from 0.1% to 2%, are generallyprovided in the form of viscous liquids.

The master batches in the paste or viscous liquid form, comprising from0.1% to approximately 10% of carbon-based nanofillers, exhibit a solidscontent, except for the content of carbon-based nanofillers, generallyof between 30% and 50%, preferably between 35% and 40%.

The term “pasty composition” is understood to mean a compositionexhibiting a Brookfield viscosity ranging from 100 to 25000 mPa·s,preferably ranging from 400 to 15000 mPa·s.

The master batch can additionally comprise a water-soluble dispersingagent used to improve the dispersion of carbon-based nanofillers andalso the stability thereof over time.

The term “water-soluble dispersing agent” is understood to mean, withinthe meaning of the present invention, a compound which makes possible ahomogeneous dispersion of the nanofillers in the superplasticizer,without resulting in an excessively high viscosity during itspreparation, and also the reduction in the forming effect during themixing stages. It is a rheology-modifying additive exhibitingantifoaming properties.

The water-soluble dispersing agent according to the invention is bondedto the nanofillers, either covalently or noncovalently.

In the case where the water-soluble dispersing agent is noncovalentlybonded to the nanofillers, it can be chosen from essential nonionicsurfactants.

The term “essentially nonionic surfactant” is understood to mean, withinthe meaning of the present invention, a nonionic amphiphilic compound,for example mentioned in the work McCutcheon's, 2008, “Emulsifiers andDetergents”, and preferably having an HLB (hydrophilic/lipophilicbalance) of 13 to 16, and also block copolymers including hydrophilicblocks and lipophilic blocks and exhibiting a low ionicity, for example0% to 10% by weight of ionic monomer and 90% to 100% of nonionicmonomer.

For example, in the context of the present invention, the water-solubledispersants noncovalently bonded to the nanofillers can be chosen from:

(i) esters of polyols, in particular:

-   -   esters of fatty acid and of sorbitan, which are optionally        polyethoxylated, for example surfactants of the Tween® family,    -   esters of fatty acids and of glycerol,    -   esters of fatty acids and of sucrose,    -   esters of fatty acids and of polyethylene glycol,

(ii) polysiloxanes modified by polyethers,

(iii) ethers of fatty alcohols and of polyethylene glycol, for examplesurfactants of the Brij® family,

(iv) alkyl polyglycosides,

(v) polyethylene/polyethylene glycol block copolymers.

In the second case, when the water-soluble dispersing agent iscovalently bonded to the nanofillers, it is preferably a hydrophilicgroup, advantageously a polyethylene glycol group, grafted to thenanofillers.

Mention may be made, as examples of commercial products which can beused, of the wetting and dispersing agent Tego® 750W from Evonik or theadditive Rhealis™ DFoam sold by Coatex.

Process for the preparation of the master batch according to theinvention

The master batch can be prepared in a single stage (i), by kneadingcarbon-based nanofillers in a kneader with at least onesuperplasticizer, optionally in the presence of a water-solubledispersing agent.

According to a first embodiment of the invention, the master batch isconcentrated and solid and can be shaped by extrusion (stage (ii)), inorder to be used directly in the application envisaged, or redispersedin at least one superplasticizer, identical to or different from thepreceding one, (stage (iii)), in order to form a master batch in thepaste form comprising a lower content of carbon-based nanofillers.According to this embodiment, it is also possible to redisperse thesolid master batch in a water-soluble dispersing agent, which makes itpossible to avoid problems of forming and of excessively high viscosityduring this stage.

According to a second embodiment of the invention, the master batchobtained in stage (i) is provided directly in the paste form.

Advantageously, the master batch in the pasty composition form isredispersed in at least one superplasticizer, resulting in asuperplasticizer (or mixture of superplasticizers) doped withcarbon-based nanofillers (stage (iv)). This procedure makes it possibleto achieve relatively low contents, for example from 0.1% to 1%, ofcarbon-based nanofillers which are completely and homogeneouslydispersed in the superplasticizer, which can be used in a comparablefashion to a superplasticizer not comprising carbon-based nanofillers.

It is therefore not necessary to adapt the method of introduction of thedoped superplasticizer in current processes for the preparation ofconcrete.

One embodiment of stage (i) consists in carrying out the kneading of themixture by the compounding route, advantageously using a corotating orcounterrotating twin-screw extruder or using a co-kneader (in particularof Buss® type) comprising a rotor provided with flights adapted tointeract with teeth mounted on a stator. The kneading can be carried outat a temperature preferably of between 20° C. and 90° C.

In order to obtain the paste directly, it is possible to predisperse thenanofillers, for example using a deflocculator, and then to use a beadmill, resulting in the production of a completely homogeneousdispersion.

Stage (iii) can be carried out using a paddle mixer, in order to obtaina homogeneous dispersion, followed by passing through a bead mill, inorder to produce a mixture not exhibiting particles with a size ofgreater than 10 μm.

Stage (iv) is carried out simply under normal stirring, for exampleusing a paddle mixer or a low-speed mechanical mixer.

Preferably, a superplasticizer of the same nature is used in thedifferent stages of the preparation process.

A subject matter of the invention is the master batch capable of beingthus obtained according to the different alternative forms of thepreparation process and comprising carbon-based nanofillers at a contentby weight of between 0.1% and 25%, preferably between 0.2% and 20%, orranging from 0.1% to 1%, with respect to the total weight of the masterbatch, it being possible for said master batch to additionally comprisea water-soluble dispersant as defined above.

Use of the Master Batch to Introduce Carbon-Based Nanofillers

The process for the introduction of carbon-based nanofillers into thecement according to the invention consists in introducing, withconventional devices, the master batch and the water which will be usedduring the mixing operation, separately or as a mixture, directly intothe kneading appliance, such as a concrete mixer, comprising the cement.

The curable inorganic system, such as cement, is generally mixedbeforehand with a material, such as sand, in a cement/sand ratio of theorder of 1:3. Without the applicant company being committed to any onetheory, it believes that the presence of the carbon-based nanofillersfacilitates the formation of an interfacial layer between the sand andthe cement; consequently, the interfaces become more compact and reducethe appearance of cracks and crevices.

According to one embodiment of the invention, the curable inorganicsystem, such as a cement, is mixed beforehand under dry conditions withhollow glass beads which are optionally treated with an organiccompound, for example of silane type, as described, for example, in thedocuments RU 2267004 or RU 2313559. In this case, the cement/beads ratioby weight ranges from 1:0.2 to 1:1. This embodiment is particularlyadvantageous for the concretes intended for drilling applications inorder to make possible good adhesion with the structures of rocks andwells and an improvement in the resistance to perforation.

According to the process of the invention, the content of carbon-basednanofillers ranges from 0.0001% to 0.02% (1 to 200 ppm) by weight,preferably from 0.0005% to 0.01% (5 to 100 ppm) by weight, with respectto the curable inorganic system, more preferably from 0.0005% to 0.005%(5 to 50 ppm), and the water/curable inorganic system ratio by weight isbetween 0.2 and 1.5, preferably between 0.2 and 0.7, and preferably from1 to 1.5 in the particular case of concretes intended to be injected. Inthese systems, the content of superplasticizer is between 0.1% and 1.5%by weight, preferably between 0.2% and 1% by weight, with respect to thecement.

The composite materials based on curable inorganic systems obtainedfollowing the process according to the invention exhibit improvedproperties related to the presence of carbon-based nanofillers: increasein the compressive strength, increase in the bending strength, decreasein the endogenous shrinkage, increase in the resistance to cold and totemperature differences, and acceleration in the hydration of thecement.

According to the invention, the use of a master batch comprisingcarbon-based nanofillers in a superplasticizer matrix simplifies themethod of direct introduction of the carbon-based nanofillers.

Thus, the process according to the invention is particularly well suitedto the preparation of denser and mechanically reinforced concretes, thepreparation of cellular concrete or the preparation of plasters.

According to the invention, the use of carbon-based nanofillers in theform of a master batch in a superplasticizer makes it possible tosignificantly improve the resistance to freezing and the diffusion ofliquid of curable inorganic systems, such as concretes, to improve theadhesion between the concrete and metal or nonmetal reinforcements orreinforcers in the form of mineral fibers or reinforcers based onpolymers in structural construction products, and/or to reduce thephenomena of microcracking due to the various stresses in structuralconstruction products.

The composite materials based on the curable inorganic systems obtainedaccording to the invention are intended for the fields of constructionand building, for preparing mortars for bricklaying or interior andexterior coatings or for manufacturing structural construction products,but also for the field of the oil industry, for drilling applications.

The invention will now be illustrated by the following examples, whichdo not have the purpose of limiting the scope of the invention, definedby the appended claims. In the examples, the percentages are percentagesby weight.

EXPERIMENTAL PART Example 1 Preparation of a Solid Concentrated MasterBatch According to the Invention

Carbon nanotubes CNTs (Graphistrength® C100 Arkema) were introduced intothe first feed hopper of a Buss® MDK 46 co-kneader (L/D=11), equippedwith a recovery extrusion screw and with a granulation device.

A 25% aqueous solution of acrylic polymer (XP 1824 from Coatex)additivated with 1% of NaOH was injected in the liquid form at 40° C.into the 1^(st) zone of the co-kneader. The set temperature values andthe flow rate within the co-kneader were as follows: Zone 1: 40° C.;Zone 2: 40° C.; Screw: 30° C.; Flow rate: 15 kg/h.

A master batch in the solid form comprising 20% by weight of CNTs wasobtained, in which the CNT aggregates are well dispersed in the XP 1824superplasticizer.

Example 2 Preparation of a Master Batch in the Pasty Composition FormAccording to the Invention

The master batch obtained in example 1 and a polyether polycarboxylatesodium salt in aqueous solution (Ethacryl® HF) were used to prepare adispersion in aqueous solution comprising:

CNTs  2.5% Ethacryl HF/XP 1824 mixture, dry 37.48%  NaOH 0.12%  Water59.9%,CNTs/Ethacryl HF, dry, ratio=0.071

For this, the master batch (125 g) was gradually added to 875 g ofEthacryl HF (40% aqueous solution) in a deflocculator (70 mm paddles)and the mixture was subjected to stirring (1550 rpm) for 3 hours.

The dispersion obtained, comprising particles with a size of the orderof 100 μm, was then subjected to a treatment in a bead mill with ahorizontal chamber (Dispermat SL-M25).

The parameters used are:

250 ml chamber filled with 200 ml of 1.2-1.7 mm ceramic beads,

Back pressure chamber: 240 ml water

Speed 4000 rpm/pump 42%/750 W (power measured)/14.2 m/s/2.5 Nm

Cooling of the chambers of the bead mill with water from thedistribution network (20° C.)

Splayed circulation of the product for 10 mn.

Approximately 800 g of a pasty composition comprising 2.5% of CNTs notexhibiting particles with a size of greater than 10 μm were recovered.

The bead mill was cleaned and rinsed by splayed circulation with wateruntil the water was clear.

Example 3 Preparation of a Master Batch in the Pasty Composition FormAccording to the Invention

The master batch obtained in example 1 and a dispersing agent in aqueoussolution (Tego 750 W) were used to directly prepare the pastycomposition comprising 2.5% of CNTs. The dispersion was obtained from:

Tego 750 W (dry content of 40%) 110 parts  Master batch of example 1 20parts Water 30 parts

The dispersion was produced in a deflocculator comprising 70 mm paddlesover 3 hours.

After 3 hours, the dispersion foams slightly and the Kreps viscosity,measured using a Lamy Rheology viscometer (measured at 30 seconds at 200rev/min), is 90 KU (i.e. 1200 mPa·s) at 20° C. At t+1 day after thedispersion, the dispersion has completely defoamed and the viscositymeasured is 64 KU (i.e. 390 mPa·s) at 20° C.

The paste thus prepared can be easily used to dope a superplasticizer.

Example 4 Preparation of a Master Batch in the Pasty Composition FormAccording to the Invention

In this example, a pasty composition was directly prepared by dispersingCNTs in a superplasticizer using a bead mill according to the followingprocedure:

In a 2 liter vessel:

Introduction of

625 g of Ethacryl HF (40% dry)

350 g of water

25 g of Graphistrength C100 CNTs, weighed under a hood suitable for theweighing of CNTs;

Predispersion in the mixer comprising 70 mm paddles for 2 to 3 hourswith stirring at 1500 rpm;

Transfer of this predispersion to the bead mill;

Monitoring of the quality of dispersion with a North bar (particles<10μm) and visual observation between slide-cover glass after dilution to1% CNTs equivalent.

The dispersion is correct at the mill outlet from the first pass;approximately 800 g of paste comprising 2.5% of CNTs dispersed in theEthacryl HF were recovered.

Example 5 Incorporation of CNTs in a Reference Concrete Based onPortland Cement

The pasty composition comprising 2.5% of CNTs obtained in example 2 wasintroduced into commercial Ethacryl HF with stirring in a mixer ofdeflocculator type (400 revolutions per minute at ambient temperaturefor several minutes), so as to dope the superplasticizer with 0.25% ofCNTs. A doped superplasticizer comprising 0.25% of CNTs is obtainedwhich is a homogeneous and stable viscous liquid.

The doped superplasticizer can be used directly in the preparation ofconcrete.

A concrete was prepared from 450 g of cement of CEM II type, index 32.5,mixed with 1350 g of quartz sand (proportion 1:3 by weight).

4.5 g of Ethacryl HF doped with 0.25% of CNTs were introduced into 160 gof water.

The mixing of the cement/sand with the water additivated with dopedEthacryl HF is carried out directly in the cement mixer for 3 minutes.The water/cement ratio is 0.36. The doped Ethacryl HF/cement ratio is1%. The CNTs content in the cement is 25 ppm.

A concrete such that the doped Ethacryl HF/cement ratio is 0.2% and theCNTs content in the cement is 5 ppm was prepared according to the sameprocedure.

Comparative concretes were prepared using nondoped commercial EthacrylHF.

Each concrete thus prepared was placed in preforms having dimensions of40×40×160 mm densified over a vibrating table for 3 min. The concretewas then stored in the preforms at 20° C. and with a relative humidityof 100% for 24 hours.

Subsequently, the samples were taken out of the preforms and they wereconditioned under the same conditions for 27 days.

Mechanical tests in compression and in bending were carried out on thesesamples on the 28^(th) day of conditioning, according to the followingmethod: GOST 310.4-81 (“Cements. Methods of bending and compressionstrength determination”).

The results are given in graphical form in FIGS. 1 and 2.

FIG. 1, which represents the bending strength of the concrete (expressedin MPa), shows the improvement in this property when a superplasticizerdoped with 0.25% of CNTs is used, in comparison with the commercialsuperplasticizer. With 0.2% of doped Ethacryl, representing the additionof 5 ppm of CNTs with respect to the cement, the bending stress isgreater than that obtained with 1% of commercial Ethacryl HF.

FIG. 2, which represents the compressive strength of the concrete(expressed in MPa), shows the improvement in this property when asuperplasticizer doped with 0.25% of CNTs is used, in comparison withthe commercial superplasticizer. With 25 ppm of CNTs in the cementintroduced by the doped superplasticizer, an improvement of more than10% is obtained for the compressive stress.

1. A process for the preparation of a master batch comprising at leastone superplasticizer and from 0.1% to 25% by weight of carbon-basednanofillers, expressed with respect to the total weight of the masterbatch, comprising: (i) the introduction into a kneader and then thekneading of carbon-based nanofillers and of at least onesuperplasticizer, optionally in the presence of a water-solubledispersing agent, in order to form a homogeneous mixture in the solidform or in the pasty composition form; (ii) the extrusion of saidmixture in the solid form in order to obtain a master batch in the solidform; (iii) optionally the dispersion of said master batch in the solidform in a superplasticizer identical to or different from that of stage(i), or in a water-soluble dispersant, in order to obtain a master batchin the form of a pasty composition; (iv) optionally the introduction ofthe master batch in the form of a pasty composition obtained in stage(i) or in stage (iii), into a superplasticizer which is identical to ordifferent from that of stage (i) or that of stage (iii), in order toobtain a master batch having a low content of carbon-based nanofillers.2. The process as claimed in claim 1, wherein the carbon-basednanofillers are carbon nanotubes, alone or as a mixture with graphenes.3. The process as claimed in claim 1, wherein the superplasticizer ischosen from: sulfonated salts of polycondensates of naphthalene andformaldehyde, commonly known as polynaphthalenesulfonates ornaphthalene-based superplasticizers; sulfonated salts of polycondensatesof melamine and formaldehyde, commonly known as melamine-basedsuperplasticizers; lignosulfonates having very low sugar contents;polyacrylates; products based on polycarboxylic acids, in particularpolyether polycarboxylate salts; and their corresponding aqueoussolutions.
 4. The process as claimed in claim 1, wherein thewater-soluble dispersant is noncovalently bonded to the carbon-basednanofillers and is chosen from essentially nonionic surfactants, such asselected from: (i) esters of polyols, in particular: esters of fattyacid and of sorbitan, which are optionally polyethoxylated, esters offatty acids and of glycerol, esters of fatty acids and of sucrose,esters of fatty acids and of polyethylene glycol, (ii) polysiloxanesmodified by polyethers, (iii) ethers of fatty alcohols and ofpolyethylene glycol, (iv) alkyl polyglycosides, and (v)polyethylene/polyethylene glycol block copolymers.
 5. The process asclaimed in claim 1, wherein stage (i) results directly in thepreparation of a master batch in the form of a pasty composition.
 6. Theprocess as claimed in claim 1, wherein stage (iii) is carried out usinga water-soluble dispersant.
 7. The process as claimed in claim 1,wherein the superplasticizer is identical in all the stages.
 8. A masterbatch comprising at least one superplasticizer and carbon-basednanofillers at a content by weight of between 0.1% and 25%, with respectto the total weight of the master batch, capable of being obtainedaccording to the process as claimed in claim
 1. 9. The master batch asclaimed in claim 8, wherein it comprises from 0.1% to 1% by weight ofcarbon-based nanofillers, with respect to the total weight of the masterbatch.
 10. The master batch as claimed in claim 8, wherein it comprisesa water-soluble dispersant.
 11. A process for the introduction ofcarbon-based nanofillers into a curable inorganic system, comprising atleast the stage of introduction of water and of a master batch asclaimed in claim 8, separately or as a mixture, into a kneadingappliance comprising at least one curable inorganic system, in order toensure a content of carbon-based nanofillers ranging from 0.0001% to0.02% by weight, with respect to the curable inorganic system, and awater/curable inorganic system ratio by weight ranging from 0.2 to 1.5.12. The process as claimed in claim 11, wherein the curable inorganicsystem is a cement base, as described in the standard EN-197-1-2000. 13.The process as claimed in claim 11, wherein the curable inorganic systemis a cement, optionally mixed with a material such as sand or hollowglass beads.
 14. A composite material based on a curable inorganicsystem capable of being obtained according to the process as claimed inclaim
 11. 15. (canceled)
 16. A method of improving the resistance tofreezing and to the diffusion of liquid of a curable inorganic system,the method comprising adding the master batch as claimed in claim 8, forimproving the resistance to freezing and to the diffusion of liquid ofthe curable inorganic system.
 17. A method of improving the adhesionbetween a curable inorganic system and metal or nonmetal reinforcementsor reinforcers in the form of mineral fibers or reinforcers based onpolymers in structural construction products, the method comprisingadding the master batch as claimed in claim 8, for improving theadhesion between the curable inorganic system and metal or nonmetalreinforcements or reinforcers in the form of mineral fibers orreinforcers based on polymers in structural construction products.
 18. Amethod of reducing the phenomena of microcracking due to the variousstresses in structural construction products, the method comprisingadding the master batch as claimed in claim 8, for reducing thephenomena of microcracking due to the various stresses in structuralconstruction products.